The actions of avermectin on crayfish nerve and muscle.

Avermectin is a potent anthelmintic, insecticide and acaricide, which is thought to act by opening GABA (gamma-amino butyric acid)-mediated chloride channels. The effects of avermectin on a crayfish nerve cell (stretch receptor neuron) were compared with those on a muscle (dactyl abductor). Concentrations above 10(-7) M caused a conductance increase and a slight reduction in GABA sensitivity in both nerve and muscle. Lower concentrations potentiated the effect of GABA in muscle, but not in the nerve cell.